Gallium-induced inhibition of the photorefractive properties of sillenite crystals

The optical, photochromic, and photorefractive properties of Ga-doped Bi12TiO20 (BTO:Ga) and Bi12Gax Bi1-xO19.5 (BGaO) crystals have been compared. The dispersion of the refractive index of each crystal has been determined in the visible and the near-infrared regions. The static dielectric constant of BGaO is epsilon(r) = 50.4. A photochromic effect that is stable at room temperature has been observed to increase with Ga concentration. Another photochromic effect that is unstable at room temperature has been observed in BTO:Ga and BGaO; the latter photochromic change is independent of the Ga concentration and has been associated with the presence of shallow traps. The photorefractive sensitivity and the photorefractive gain of the crystals decrease with increasing Ga concentration. A model assuming the presence of deep and shallow traps is used to describe qualitatively the writing and the erasure kinetics observed. (C) 1996 Optical Society of America